Self-tuning approach to optimization of excitation angles for switched-reluctance motor drives

Abstract

A new approach to automatic control of excitation parameters for the switched reluctance motor (SRM) is presented. A turn-on and Turn-off angles play important roles in developing electromagnetic torque in SRM. The value of excitation angles are usually variable and depend upon the motor speed and other parameters of the inverter that excites the SRM. As the motor speed increases the shape of the current waveform, changes in such way that limits the production of motoring torque. At high speeds, it is possible for the phase current never reaches the desired value due to motor phase inductance, therefore, the torque falls off. In order to remedy this problem, the phase turn on angle is advanced in such way that the phase commutation begins sooner. Advancing the commutation angle offers the advantages of getting the current into the phase winding while the inductance of the phase is low, and also of having a little more time to get the current out of the phase winding before the rotor reaches the negative torque region. Since the SRM drive is a variable speed motor then, the amount of advancing for the turn on and turn off angles should be accomplished automatically according to the speed of the motor. In order to optimize the timings of the Turn-on and Turn-off angles, on line rotor position is detected and then the angular speed is calculated. The computed optimum timing of excitation angles are then fed into a commutation logic block. This block decides on the proper phase winding to be energized. Control of the excitation angles result in either positive net torque for motoring or negative net torque for generating which optimizes the torque at high speed. This technique is then applied to an experimental SRM drive system in speed ranging from 0 to 8000 rpm. Experimental operation shows this technique provides much higher torque production for the motor.